Invention pertains to building constructions like ceiling and floor slabs and their elements – plates, ribs and bridge girders. These slabs could be made with one direction span or contour supported. A material layer working under compression load (1) is located in a compression zone of the construction. Reinforcement containing tensioned (2) and compressed (3) bars are located in an extension zone. The compressed bars have two parts with right and left threads located in collar nuts (5). In such a way it is possible to change the length of the compressed bars and transfer posttensioning force to the tensioned bars (3) of the external reinforcement.